It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Under every hair there is janabah (impurity), so wash the hair and clean the skin thoroughly."
Al-Harith bin Wajih is alone in narrating this hadith with a connected chain, and the hadith scholars have criticised him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 827